Seaweeds and soy are two commonly eaten foods in Asia. Both have been reported to affect thyroid function, seaweed because of its iodine content and soy because of its goitrogenic effect. Twenty-five healthy postmenopausal women (mean age 58 years) completed a double-blinded randomized crossover study. Ten capsules (5 g/day) of placebo or seaweed (Alaria exculenta), providing 475 ug of iodine/day, were consumed daily for 7 weeks. A powdered soy protein isolate (Solae Co., St. Louis, MO) providing 2 mg of isoflavones/kg of body weight, was given daily during the last week of each treatment arm. On average, this provided 141.3 mg of isoflavones/day and 67.5 g of protein/day. Blood samples and 48-hour urine samples were collected before and after each intervention period, and urinary I/C (ug of iodine/g of creatinine) and serum thyroxine, free thyroxine index, total triiodothyronine, and thyroidstimulating hormone (TSH) were measured. Seaweed ingestion increased I/C concentrations (P < .0001) and serum TSH (P < .0001) (1.69 +/- 0.22 vs. 2.19 +/- 0.22 uU/mL, mean +/- SE). Soy supplementation did not affect thyroid end points. Seven weeks of 5 g/day seaweed supplementation was associated with a small but statistically significant increase in TSH. Soy protein isolate supplementation was not associated with changes in serum thyroid hormone concentrations.
Published in Journal of Medicinal Food, Volume 10, Issue 1, 2007, pages 90-100.
Teas, J., Braverman, L.E., Kurzer, M.S., Pino, S., Hurley, T.G., & Hébert, J.R. (2007). Seaweed and Soy: Companion Foods in Asian Cuisine and Their Effects on Thyroid Function in American Women. Journal of Medicinal Food, 10(1), 90-100. DOI: 10.1089/jmf.2005.056
This is a copy of an article published in the Journal of Medicinal Food © 2007 Mary Ann Liebert, Inc. and Korean Society of Food Science and Nutrition; Journal of Medicinal Food is available online at: http://online.liebertpub.com.